Polyvinylidene fluoride (PVDF) is a chemically resistant engineering plastic. PVDF and its copolymers have been used in many high performance applications. While PVDF films can be made to be transparent, they still have some degree of haziness, producing a product that is less than optically clear. There is a need for an optically clear PVDF or PVDF copolymer that retains the chemical resistance of PVDF
U.S. Pat. No. 5,140,082 discloses a vinylidene fluoride/trifluoromethyl ethylene copolymer (3,3,3-trifluoropropene)(TFP). Synthesis by solution, suspension and emulsion polymerization are described, with all the TFP in the initial charge. The copolymer has excellent weather resistance, corrosion resistance and electrical characteristics. The reference is silent on optical clarity.
2,3,3,3-tetrafluoropropene copolymers have been formed with other monomers, as described for example in JP 10310712, JP 09288915, JP 63284250, and JP 58164609.
There is a desire to form copolymers of 2,3,3,3-tetrafluoropropene and vinylidene fluoride, to take advantage of properties that can be brought by polymers of these monomers.
Surprisingly it has now been found that copolymers of vinylidene fluoride and 2,3,3,3-tetrafluoropropene having a wide range of 2,3,3,3-tetrafluoropropene levels can be synthesized to produce copolymers having excellent optical properties. Additionally films of the copolymer are extremely flexible and tough, and have a high melting point.
Interestingly, copolymers of vinylidene fluoride and (2,3,3,3 tetrafluoropropene) were found to form much more readily than those of vinylidene fluoride-3,3,3 trifluoropropene. While not being bound by any particular theory, it is believed that the existence of (tertiary) hydrogen on 3,3,3 trifluoropropene structure inhibits copolymerization reaction causing process delays and increase in initiator usage which in turn adversely affect product quality. In the 2,3,3,3 tetrafluoropropene structure, on the other hand, (tertiary) hydrogen is replaced by a fluorine atom eliminating reaction inhibition. Comparable copolymerization reactions shows a large decrease in reaction time and initiator usage for vinylidene fluoride-2,3,3,3 tetrafluoropropene polymerization compared to vinylidene fluoride-3,3,3 trifluoropropene reactions. Further, there is significant improvement in product color (by heat pressed plaques) for the 2,3,3,3 tetrafluoropropene copolymer.